Protective arrangement



April 12, 1932. HEWLETT 1,854,031

' PROTECTIVE ARRANGEMENT Filed June 28, 1929 Fig.1.

Fig.2.

Inventor". EdwaTd.M Hewlett, 8 His Attorneg.

f 35 without sacrificin Patented Apr. 12, 1932 UNITED STATES PATENT OFFICE EDWARD. M. HEWLETT, OF SGHENEC'IADY, NEW YORK, ASSIGNOR T GENERAL ELEG- TRIO COMPANY, A CORPORATION OF NEW YORK PROTEOIIVE ARRANGEMENT Application filed June as,

My invention relates to improvement in protective arrangements for electric circuits and more particularly such as embody fusible elements for effecting .a circuit interruption on' the occurrence of abnormal circuit conditions.

Where fuses, particularly of the expulsion type, are chosen so as to be relatively sensitive, the fuse is apt to run at a temperature destruc 1n tive to the fuse holder. Moreover, in case of relatively high voltages, as in the protection of potential transformers for instruments, meters, relays, etc., the current may be so small as to require a fusible element of 'such a, small cross-section as to be mechanically weak and inconvenient to handle. Furthermore, with such a small cross-section, the ag 111g or may result ina circuitinterruption under normal conditions. If the cross-section is increased, then the sensitivity is destroyed and the expulsion effect may be lost since the fuse, instead of melting throughout its length sub-' stantially instantaneously, may merely break at the weakest point and gradually melt. In this case a destructive-arc is maintained, the circuit is not interrupted-and damage results to the fuse holder and probably other apparatus. In view of these difficulties, an object so of my invention is to provide an improve protective arrangement for amplifying the fusing effect only on the occurrence of abnormal circuit conditions whereby a mechanically and electrically strong fuse may be used the safety or sensitivity of the protection esired.

My invention will be better understood from the following description when considered in connection with the accompanying 4 drawings and its will be pointed out in the appended claims. 7 In the accom anying drawings Fig. 1 illustrates, partly 'agrammatically an embodiment of my invention and Fig. 2 illustrates diagrammatically a modification of a part (I); the embodiment of my invention shown in the embodiment of my invention shown in Fig. 1, an'electric circuit 4, which may be energlaed from a bus or feeder 5, includes a deterioration of the fusible element 1 1929. Serial No. 374,481.

winding of a potential transformer 6 and is arranged to be controlled by a. fuse 7 in accordance with my invention by means of which the current inthe fusible element 8 is suitably amplified on the occurrence of abnormal conditions, for example on the circuit 4 or on the transformer 6 or a circuit 9 supplied thereby.

. 10 of insulating material and a cap 11, which may be of conducting material, suitably secured thereto. The cap 11 serves as a housing for the fusible element 8, one end of. which is suitably insulated from-the cap by means such-as insulating blocks 12 and 13. Between these are mounted conducting members, such as disks 14 which may be centered inrecesses in the blocks 12 and 13 so as not to touch the cap 12. To hold thefusible element 8 in'place so as to be easily replaceable, a screw plug 15 may be employed to clamp the bearingvplate 16, the blocks 12 and 13, and the disks 1 f tightly against each other and the baseof the cap 11. Within the tube" 10 is mounted a conducting element 17 connected in the circuit 4 to be protected and-at one end to an intermediate point of the fusible element 8. The conducting element 17 may also be a fusible element thus providing two (1 fusible portions for the fuse. In order to asthe fusible elements upon sist in separating rupture, a spring 18 may be connected to the base of the, tube and. to a point on the conducting element 17. In order to amplify the current supplied to the fusible element 8 on the occurrence of abnormal circuit conditions, I provide in accordance with my inven 'on transforming means 19 which, as shown, is arranged to supply to the fusible element 8 on the occurrence of current in excess of a predetermined value in the circuit 4, a current greater than the current in this circuit. For this purpose the magnetic circuit of the transforming means is arranged normally to have a high reluctance so that the coupling between the primary and secondary windings dependent on' and 20 and 21is normally relatively weak but the if any,

curs. As shown this change in reluctance is accomplished by providing within the magnetic structure 22 and in the magnetic circuit of the windings 20, 21, an air gap under 4, the primary winding 20 may be connected in series relation with this circuit and to an intermediate point of the secondary winding 21 such as the electricalcenter or middle thereof, while the fusible element is connected across the secondary winding through the cap 11, the disks 14, the plate 16 and the plug 15 through the conductors 26, one of which passes through an insulator 27' in the cap 11. In this way the current in the circuit 4 flows in parallel through the -two halves of the secondary winding 21 and-the resultant magnetic effect is substantially zero. Due to the normally weak inductive coupling between the windings 2O, 2lpractically little, current appears in the parts of the fusible element 8 on either side of the conductin element or lead 17 in excess of onehalf 0 the current in the circuit 4.

On the occurrence of abnormal circuit conditions causing a current in the circuit 4 sufiicient to pick up the armature 23, the reluctance of the magnetic circuit of the windings is so decreased that their resulting strong inductive coupling produces a surge of current in the winding 21. This current is superimposed on the circuit current already fiowing in the fusible element 8 which consequently melts and releases the conducting element 17 which under the force of the spring 18.is quickly expelled-from the tube,

If the element 17 is also of fusible material, it

may also melt on the occurrence of a sulficiently large current and thus expedite the expelling action and more quickly effect the arc interruption.

Inasmuch as the current supplied to the fusible element may be amplified to any desired degree on the occurrence of fault conditions, the fusible element 8 may be 0 large cross-section for mechanical strength without destructive heating under normal operation. This is likewise true of the element 17, if of fusible material, since it is relied upon only for fault currents sufiiciently great, without amplification, to cause its rupture.

Instead of using a transforming means 22 with the windings arranged as in'Fig. 1, an

. auto-transformer may be used as shown in Fig. 2. In this case also the primary winding is in the circuit to be protected and the secondary winding supplies the fusible element 8. 1

While I have shown and described my invention in considerable detail, I do not wish to be limited to the exact arrangements shown, but seek to cover in the appended claims all those modifications that fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by' Letters Patent of the United States, is:

1. In combination, an electric circuit, a fusible element connected in said circuit, transforming means for supplying to said fusible element on the occurrence of abnormal circuit conditions a current dependent on and greater than the current in said circuit including a normally high reluctance magnetic circuit, a Winding connected in said electric circuit and a cooperating winding conected to supply said fusible element, an

means for decreasing the reluctance of the magnetic circuit of said transforming means on the occurrence of abnormal circuit conditions.

2. In combination, an electric circuit, a fuse in said circuit, a transformer for supplying to said fuse on the occurrence of abnormal circuit conditions a current dependent on and greater than the current of said circuit including a normally high reluctance magnetic circuit, a primary winding connected in series in said electric circuit and a secondary winding having its electrical center connected to one terminal of said primary winding, said fuse being connected across said secondary winding, a circuit lead from said fuse, and means for substantially decreasing the reluctance of the magnetic circuit of said transformer on the occurrence of current in said circuit in excess of a predetermined value.

3. In combination, an electric circuit, a fuse directly connected in said circuit, a transformer for supplying to said fuse on the occurrence of abnormal circuit conditions a current dependent on and greater than the current in said circuit including a pri-- inary winding connected in series relation with said circuit, a secondary winding connected to supply said fuse and a magnetic structure including a movable magnetic member arranged normally to be positioned to provide a relatively large air gap in the magnetic circuit of said windings and operative on the occurrence of current in excess of a predetermined value in said primary winding substantially to decrease said air p- 4. In combination, an electric circuit, a fuse directly connected in said circuit, a transformer for supplying to said fuse on the occurrence of abnormal circuit conditions a current dependent on. and greater than the current in said circuit including a primary provide a relatively large air gap in the magwinding connected in series relation with said circuit, a secondai-(y connected to supply said fuse an a magnetic structure 1nclu 'ng an armature. arranged normally to netic circuit of said windlngs and operative on the occurrence of current in excess of a predetermined value in said circuit substantially to decrease said air gap.

5. In combination, an electric circuit, a fuse includmg two portlons, one connected 1n series in said circuit and to an intermediate point of the other portion, transforming secondary winding connected across said other fuse portion, a primary winding connected in series relation with said circuit and to said secondary winding and a normally high reluctance magnetic structure for said windings, and means for substantially decreasing the reluctance ofsaid structure on the occurrence of abnormal circuit conditions. I

6; In combination with a potential transformer, a fuse connected in circuit with a winding of said transformer, transforming means for su plyin'g'to said fuse on theoccurrence of a normal conditions on said potential transformer a current dependent on and greater than the current in said potential transformer winding including a primary winding connected in series relation with the potential'transformer winding, a secondary winding connected to supply the fuse and a normally low reluctance magnetic circuit for said primary and secondary windings, and means for decreasing the reluctance of said magnetic circuit on the occurrence of current in excess of a predetermined value in said potential transformer winding.

7. In combination, an electric circuit, a fumble element connected in said circuit,

transforming means for supplying to said fusible element on the occurrence of abnormal circuit conditions a current dependent on and greater than the current in said circuit, including a winding connected in said circuit and a cooperating winding connected to supply said fusible e ement, said windings bein normally loosely inductively coupled an means for increasing the inductive cou ling ofsaid windings on the occurrence of a normal circuit conditions.

8. A protective arrangement for an electric circuit including a transformer having its primary winding connected in seriesin the circuit, one terminal of said primary winding being connected to the electrical centerof the secondary winding of the transformer, said transformer windings being normally, loosely, inductively coupled, a fuse connected across said secondary winding, a

circuit lead from said fuse, and means for mcreasing the inductive coupling of said transformer windings on the occurrence of abnormal circuit conditions. i

In witness whereof, I have hereunto set my hand this 27th da of June, 1929.

' ED ARD M. HEWLETT. 

